This invention relates generally to brush seals and more particularly to apparatus and methods for positively adjusting clearance between a brush seal and an opposing component against which the brush seal bears to form the seal.
Brush seals are commonly used to minimize leakage through a gap between parts or components which are to be sealed to one another. For example, brush seals are commonly used in rotating machinery such as steam and gas turbines used for power generation. Typically, the brush seals minimize leakage between regions at different pressures on opposite sides of the seal. As a specific example, a steam turbine may employ a brush seal for minimizing leakage of steam between a stationary component and a rotating component such as a rotor.
While brush seals are discussed herein in a preferred embodiment with respect to sealing between stationary and rotating components, it will also be appreciated that brush seals can be applied to seal components which are non-rotating and may be irregularly shaped. For example, a brush seal may be used to seal between a combustor transition piece and a sealing cap of a first stage nozzle in a gas turbine. In a typical application of a brush seal between stationary and rotating components, however, the brush seal comprises a plurality of arcuate segments, each segment conventionally including a pair of plates with a plurality of brush bristles disposed between the plates. The plates and proximal ends of the brush bristles between the plates are typically welded to one another, forming a completed brush seal segment. Opposite ends of the bristles project from between the plates, terminating in free ends or tips engaging and forming a seal with the other component, typically the rotating component. The arcuate brush seal segments are typically disposed in a groove of the stationary component and may have a spring between the component and the segment biasing the segment for movement between the opposing sealing components, e.g., for movement toward the rotating member.
It has been found, however, that because of stack-up tolerances and machine-to-machine variations, it is very difficult to achieve accurate clearance control, even with brush bristles biased by a spring toward the opposing sealing component. Also, it is common that for the same machine, the sealing clearance may be different from the bottom half to the upper half of the machine. For example, gravity affects the brush seal segments in the semi-circular upper and lower casings of a steam turbine tending to engage and disengage, respectively, the bristle tips relative to the rotor. These operating clearance variations result in performance changes in different applications. Additionally, brush seal leakage performance also tends to degrade with time and progressive bristle wear.
In accordance with a preferred embodiment of the invention, an adjustable clearance brush seal is provided wherein the sealing clearance between the parts or components being sealed may be positively controlled, particularly during operation of the associated machine, and from locations external to the machine. For example, the brush seal may be provided in arcuate brush seal segments disposed in a groove of a stationary component with the bristles in opposition to, and engaging, the rotating component. The seal clearance between the bristles and the opposing component can be positively controlled. The seal clearance is the degree of interference between the brush bristles and the opposing sealing component, as well as any gap between the tips of the bristles and the associated sealing component, e.g., where it may be desired to maintain a gap permitting flow between opposite sides of the seal. To accomplish the foregoing, a member or members formed of a thermally expansible or contractible material are disposed in controlling relation to the brush seal in the component carrying the brush seal to control the location of the brush seal vis-a-vis the seal component engaged by the bristle tips. For example, each member may comprise one or more pins or sleeves carried by the stationary component and disposed in the groove between the stationary component and the brush seal to extend in a generally radial direction. Upon application of heat to the thermal material of the members, the members tend to elongate, displacing the brush seal segment radially toward the opposing seal component. Conversely, when the temperature of the members is lowered, any interference between the opposing seal component and the bristles of the brush seal tend to displace the brush seal segment in an opposite direction toward the component in which the brush seal is mounted. Consequently, the opposite ends of the members need not be secured to either the component or the brush seal. Alternatively, one or both ends of the members may be secured, for example, by welding, to the component mounting the brush seal and to the brush seal per se, whereby positive control of the brush seal can be effected to move the brush seal in opposite directions responsive to the differential heat applied to the members.
More particularly, and as noted previously, the members may comprise pins or hollow sleeves having heating elements about the pins or within the sleeves. The heating elements preferably comprise electrically actuated elements which can be controlled through suitable circuitry employing, for example, a rheostat. By adjusting the rheostat to control the magnitude of the heat supplied to the members, the members can be differentially expanded or contracted. A still further alternative may comprise a circumferentially extending member, e.g., a band, having a heating element contained within the band or about the band for expanding or contracting the band and, hence, displacing the brush seal segment toward or away from its opposing seal component.
The members are formed of materials having a high thermal coefficient of expansion and the electric heating elements may be embedded in or about the materials. By increasing or decreasing the power supplied to the heating elements, the pins or bands expand or contract, respectively, moving the seal segments toward or away from the opposing seal component, respectively. Consequently, the user may adjust the power setting to achieve the desired clearance. This also can be accomplished externally of the machine and while the machine is in operation. A particular advantage of the invention resides in elimination of a need for tight tolerances for the seal and its mounting, thereby easing machining constraints and reducing costs.
In a preferred embodiment of the invention, apparatus for adjusting a seal between two components includes a brush seal carried by one of the components for disposition between the two components and having a plurality of bristles projecting from the brush seal, with free ends of the bristles terminating in bristle tips in engagement with the other of the components forming a seal between the components. The brush seal is mounted for movement relative to one component and toward and away from the other component. A member disposed between the one component and the brush seal is responsive to heat either applied thereto or removed, by expanding or contracting, respectively, thereby displacing the brush seal relative to the one component toward or away from the other component, respectively.
In a further preferred embodiment, a rotary machine includes a rotatable component and a component fixed against rotation, the components being disposed about an axis, and a seal between the components comprising an arcuate brush seal segment carried by one of the components, including a plurality of bristles projecting from the one component and having free ends terminating in bristle tips in engagement with the other of the components, forming a seal between the components. The brush seal segment is mounted for movement relative to the one component and toward and away from the other component. A member is carried by the one component for displacing the brush seal segment relative to the other component and is formed of a material thermally responsive to heat applied differentially thereto by expanding or contracting and thus moving the brush seal relative to the one component, thereby adjusting the sealing clearance between the brush seal segment and the other component.
In a still further preferred embodiment of the invention there is provided in a seal between adjacent components including a brush seal carried by one of the components for movement relative to the one component toward and away from a second one of the components, the brush seal having a plurality of projecting bristles terminating in bristle tips in engagement with the second one of the components, a method of positively controlling the brush seal position relative to the one component comprising the steps of disposing a member between the brush seal and the one component which is formed of a thermally responsive material; and applying heat at different temperatures to the member of thermally responsive material to expand or contract the member and thereby move the brush seal relative to the one component and toward or away from the second component.